This application relates to the art of making polybenzazole films, three-dimensional shaped articles and other shaped articles except for fibers.
It is well-known to polymerize polybenzazole polymers in polyphosphoric acid solutions, so that an acid dope is formed. See, e.g., Wolfe et al., U.S. Pat. No. 4,533,693 (Aug. 5, 1985) which is incorporated herein by reference. Frequently, the resulting polymers are not thermoplastic. However, they can be made into shaped articles such as films, coatings and net-shaped parts by: (a) forming the desired shaped article out of the dope; (b) coagulating the polymer in the shaped article; and (c) leaching (or washing) residual phosphoric acid out of the coagulated article. See, e.g., Harvey et al., U.S. Pat. No. 4,973,442 (Nov. 27, 1990), which is incorporated herein by reference.
The coagulation and leaching steps can become a significant bottleneck in a continuous production process, because they are very time-consuming. Commercially desirable films should contain no more than about 2000-2500 ppm phosphorus, and film for very sensitive uses should contain 250 ppm phosphorus or less. On the other hand, the Harvey patent shows that film washed in water for 5 minutes contains 4 weight percent phosphorus, and film washed for 48 hours still contains 0.8 weight percent phosphorus. The long leaching times needed to reach acceptable levels of phosphorus are unmanageable in a commercial production.
What is needed is an accelerated process to coagulate and leach non-fiber polybenzazole articles.